Generally, a GaN-based nitride semiconductor is being applied to an optic device such as a blue/green LED, and an electronic device having a characteristic of a high speed switching and high outputting in its application field, such as Metal Semiconductor Field Effect Transistor (MESFET) and High Electron Mobility Transistor (HEMT). Specifically, the blue/green LED is in mass-production, and its worldwide sale is being exponentially increased. Such a GaN-based nitride semiconductor light emitting device is mainly grown on a sapphire substrate or a SiC substrate. Additionally, a polycrystalline thin film of an AlyGa1-yN layer is grown as a buffer layer on the sapphire substrate or the SiC substrate at a low growth temperature. After that, an undoped GaN layer, a Si-doped n-GaN layer or a combination thereof is grown on the buffer layer at a high temperature to manufacture the nitride semiconductor light emitting device having an n-GaN layer functioning as a first electrode contact layer and a magnesium-doped p-GaN layer, which is formed over the first electrode contact layer to function as a second electrode contact layer. Further, a light emitting layer is a PN junction diode having a sandwich structure in which an active layer with a multi quantum well structure is interposed between the first electrode contact layer and the second electrode contact layer.
However, the above-constructed nitride semiconductor light emitting device has a drawback in that a very high crystal defect of about 108 cm3 is generated at an interface of the substrate and the buffer layer and accordingly, an electric characteristic of the nitride semiconductor light emitting device, specifically, a current leakage is increased under a reverse bias condition, thereby having a critical influence on a device reliability.
Further, the nitride semiconductor light emitting device has a disadvantage in that it is not applicable due to a low luminance to a large screen device requiring a high luminance. Therefore, a solution for improving the reliability of the light emitting device and increasing the luminance is being continuously studied.